(a) Field of the Invention
The present invention relates to an inverted type microscope which is suited for observing cells being cultivated in a culture dish, surfacial conditions of metals, minerals and so on.
(b) Description of the Prior Art
When cells 3 being cultivated in a culture dish 1 shown in FIG. 1, for example, are observed through an ordinary type microscope as shown in FIG. 3, remarkable reflection on the surfaces of cover 2 of the culture dish and culture fluid 4 makes it impossible to clearly observe the cells which are located on the bottom of the culture dish. In observing a surface 5a of a metal or mineral specimen 5 as shown in FIG. 2 through an ordinary type microscope, the microscope can be focused only on a portion of the surface 5a if said surface is not perfectly parallel with the surface 5b on the opposite side. In such a case, tedious procedures are required for refocusing the microscope each time for observing a different portion of said surface. For observing such specimens, there have been contrived inverted type microscopes which have objective lenses arranged under the specimen stage for observing through the bottom surface of said specimen stage on the top surface of which specimens such as culture dishes, minerals are to be mounted. However, such inverted tupe microscopes have a common defect that they are low in operability and a micrographing system can hardly be arranged due to the fact that the ocular is positioned lower than the specimen stage for assuring a mechanical tube length equivalent to that of the ordinary type microscopes. This defect can be eliminated by prolonging the mechanical tube length. Speaking concretely with reference to an ordinary type microscope, the mechanical tube length can be prolonged by arranging relay lenses between the contact surface 6a of the revolver 6 and the contact surface 7a of the microscope tube 7 shown in FIG. 3. Since a single negative lens group used as the relay lens system will enhance the image magnification, it is general to design the relay lens system as a combination of positive and negative lenses or negative and positive lenses. However, such a method for prolonging the distance to the image position will inevitably increase the magnification of pupil, prolong the optical tube length, cause eclipse and limit the field number.
Similarly in case of an inverted type microscope, such a relay lens system for prolonging the mechanical tube length will inevitably prolong the optical tube length, thereby making the microscope practically unusable.